Embryo

Embryo is a term used in biology to refer to the early developmental stages of a multicellular organism. In humans, it is the stage of prenatal development from the moment of fertilization until the end of the eighth week of gestational age, after which it is then referred to as a fetus.

Development

The development of the embryo follows fertilization, and continues as a cellular proliferation and cellular differentiation which leads to the development of many cell types, tissues and organs. This process is guided by the genetic information carried by the embryo's cells.

Stages of Embryonic Development

The stages of embryonic development include the zygote, morula, blastocyst, gastrula, and neurula stages. Each stage is characterized by specific cellular events and changes.

Zygote

The zygote is the initial cell formed when two gamete cells are joined by means of sexual reproduction.

Morula

The morula is an early stage embryo consisting of cells (called blastomeres) in a solid ball contained within the zona pellucida.

Blastocyst

The blastocyst is a structure formed in the early development of mammals, and it possesses an inner cell mass, which forms the organism, and an outer layer of cells, or trophoblast, which forms the placenta.

Gastrula

The gastrula is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a multilayered structure known as the gastrula.

Neurula

The neurula is a stage in vertebrate embryonic development, in which the neural tube forms.

See Also

• Fertilization
• Prenatal development
• Cellular differentiation
• Zygote
• Morula
• Blastocyst
• Gastrula
• Neurula

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